English Abstract: Social interactions unfold against a backdrop of mutual reliance. Though it may be wholly implicit, this reliance guides our actions and helps ensure the smooth operation of social life. It makes our interactions foreseeable, provides a baseline of expectation in social relations, and builds confidence that appearances reflect reality. In law, the idea of “legitimate reliance” is ubiquitous. When it operates, it gives legal effect to situations of apparent rights, apparent powers, or voluntary undertakings in private law interactions. This text studies the role and the scope of legitimate reliance in the law of obligations, in order to determine whether there is room for such a principle within Quebec civil law. If expanded into a general principle of Quebec civil law, legitimate reliance would undermine the apparent coherence of the law of obligations, which has until now been built on a foundation of individual freedom. From a traditional point of view, such a principle appears at once suspect, shapeless, and burdensome. It seems unlikely to establish itself as part of a general theory of obligations, faced with such resistance. Nonetheless, it can stands as a rich and fruitful counter-theory.